The invention relates to a brush seal for a gas turbine, in particular an aircraft engine.
Brush seals are used in particular to prevent or at least substantially reduce leakage between a stationary part (hereinafter also called a stator) and a rotating part (hereinafter also called a rotor). A known brush seal comprises a wire ring with the bristles placed around it. A c-shaped clamping ring is often used for affixing the bristles to the wire ring. The bristles usually lie in a plane running perpendicular to the axis of rotation of the rotating part. In order for the bristles not to be axially displaceable—based on the axis of rotation of the rotating part—toward the side where the lower pressure prevails, i.e., toward the downward pressure side, a means of fixation must be provided. To do so, a sufficiently stable annular support plate is arranged on the downstream side of the bristles. The annular support plate must be designed to be shorter than the bristles in the radial direction toward the rotating part so that there is a clearance between the lower edge of the support plate and the rotating part. In contrast with that, the bristles scrape along the surface of the rotor.
Such a brush seal, which is known from the prior art, is illustrated in FIG. 1, for example. FIG. 1 shows a meridian section, based on the axis of rotation of the rotor (not shown here) through a brush seal 2. In the diagram in FIG. 1, the flow is from left to right, so that the pressure p1 in FIG. 1 is higher at the left of the brush seal than the pressure p2 at the right of the brush seal. The brush seal 2 comprises a support ring 4 extending essentially radially in this sectional view and an annular holding plate 6, which extends essentially radially, and they are connected to one another in the radially outer region 8. In the radially inner region 10 between the support ring 4 and the holding plate 6 a receptacle 12 is provided for the bristles 14. These bristles 14 are coiled around a wire ring 16 and are held on the wire ring 16 by a c-shaped clamping ring 18. The elements 14 to 18 are arranged in the receptacle 12 in such a way that the clamping ring 18 is clamped by the support ring 4 and the holding plate. The support ring 4 has a stiff annular support element 20 directed inward radially, with a lateral surface 21 directed inward radially and an annular mounting plate 22 arranged on the outside radially from the support element 20 and offset therefrom in the downstream direction. The mounting plate 22 is connected here on its downstream side to an L-shaped stator section 24. The bristles 14 protrude radially inward over the lateral surface 21, so that the radially inward directed end 25 of the bristles 14 scrape against the surface 30 of a rotor 26. A central region 28 of the bristles 14 is in contact with the support element 20. A clearance S is provided between the lateral surface 21 of the support element 20 and the surface 30 of the rotor 26.
In the event of damage to the gas turbine, the rotor can shear off radially to a much greater extent than would be expected during normal operation. This may occur in particular when a rotor blade breaks off from the rotor, for example, when a bird strike results in loss of a fan blade in an aircraft engine. Then the rotor is no longer balanced, so the motion of the rotor around its original axis of rotation becomes eccentric. Then, if the clearance S between the support element and the rotor has been designed to be very small, this may result in damage to the rotor because the support element cuts into the rotor. In the worst case, this may result in breakage of the rotor. To reduce the damage to the rotor, the lateral surface of the support plate may be coated accordingly. However, only very small layer thicknesses are possible here. However, if the clearance between the support element and the rotor has been designed to be too large, this increases the bundle leakage so that the sealing effect and thus also the efficiency of the gas turbine are reduced.
The present invention is thus based on the object of providing a brush seal that will not damage the rotor in a damage incident involving the gas turbine and at the same time will offer the best possible sealing effect during normal operation.
The invention relates to a brush seal for a gas turbine, in particular an aircraft engine having at least one support ring, which has a support plate and a support structure, in particular an annular support structure that is arranged downstream with respect to the support plate and having a plurality of bristles, which are arranged upstream with respect to the support ring and whose ends protrude radially inward beyond the support plate. The support structure is designed here so that, on occurrence of a scraping force acting radially outward on the lateral surface of the support structure facing radially inward, the latter will yield, preferably with a spring elastic effect, whereas, when an axial operating force occurs on at least one of the lateral surfaces of the support structure, the latter will withstand this axial operating force.
This support structure is designed so that with a scraping force acting on it radially from the rotor, it yields, preferably with a spring elastic property, without exerting any mentionable opposing force on the rotor, for example an opposing force of less than 100N, preferably less than 50N, more preferably less than 10N. In contrast with that, the support structure does not yield to any mentionable extent or at all when an axial operating force occurs according to the invention. In other words, in the axial direction, the support structure has a stiffness many times greater than its stiffness in the radial direction (the term “axial direction” as used here is always understood to refer to the axis of rotation of the gas turbine, whereas the radial direction is a direction orthogonal to the axial direction). The stiffness of the support structure in the axial direction in particular may be greater than that in the radial direction by a factor of at least 10, preferably at least 100, more preferably at least 1000.
This is advantageous in particular because the brush seal according to the invention thus has a scraping-tolerant design. The previous approaches prevent any scraping contact. Thus the clearance between the rotating part and the support plate may be designed to be as small as possible. The minimal clearance can also occur due to shrinkage in the initial operation of the turbine. This ensures the least bundle leakage.
The support plate, which serves in particular to support the bristles in the axial direction, may be designed to be much thinner than the support structure in comparison with the support structure adjacent to it in the axial direction (i.e., having a smaller extent in the axial direction), preferably less than half as thick, more preferably less than ⅕th as thick, even more preferably less than 1/10th as thick as the support structure. This is made possible because when the bristles adjacent to the support plate on the upstream side exert an axial force on it, so that the bristles can be supported on the support structure adjacent to them downstream; this support structure is designed to be stiff in the axial direction accordingly. This makes it possible for the support plate to be designed so that it will yield due to shearing, bending, scraping, and/or melting in particular as soon as a scraping force directed radially outward from the rotor of the gas turbine acts on the support plate, without any mentionable counterforce acting on the rotor of the gas turbine and in particular without damage to the rotor of the gas turbine, in particular notching. As described in the introduction—this case occurs easily otherwise with known brush seals for gas turbines in an emergency, for example when there is a great imbalance due to loss of a fan blade because of a bird strike, when a rotating component is deflected too much radially and comes in contact with the support plate. Furthermore, the support plate may be closed or slotted. In addition, the support plate may be segmented.
It is advantageous to place the support structure behind the support plate, as seen in the direction of flow, because this offers the option of reinforcing the support plate in the axial direction of loading (i.e., in the direction of flow) by the support structure. Thus the support plate can be designed with smaller dimensions in the axial direction, for example, and can thus be designed to be softer in the radial direction.
Furthermore, since the clearance between the rotor of the gas turbine and one end of the support plate, which is directed radially inward, can be designed to be so small, the support plate significantly improves the sealing function of the brush seal, whereas the supporting function in the axial direction can be handled by the support structure. As described previously, the support plate can be designed to be very narrow in the axial direction and will thus yield much more easily by abrasion and/or melting when an outward directed radial force occurs. Therefore, there is hardly any notching effect of the support plate on the rotor. In particular, the support plate and the support structure may be constructed of different materials. During operation, the support plate may be in contact with the support structure.
The support structure may be made of a flexible material. The support structure here may be designed with open pores and/or may be made of a sintered material. Narrow mesh structures and/or honeycombs are also conceivable.
In another advantageous embodiment of the invention, there is a clearance between the support structure and the support plate. Furthermore, the support structure may run essentially parallel to the support plate or the support structure may be arranged on the support plate. The support plate and the support structure here may be integrally molded (form fitting, physically bonded or force locking).
This is advantageous in particular because the axial stiffness of the entire support ring can be adjusted by a clearance.
In another advantageous embodiment of the invention, the support structure has a plurality of ribs situated in a plane running essentially radially, these ribs being inclined in at least some sections at an angle (β) with respect to the radial direction, such that the angle (β) is preferably between 10° and 40°. The ribs may extend further in the axial direction than in the peripheral direction.
In another advantageous embodiment of the invention, the bristles form an angle of 40° to 60° with the radial direction. As soon as the ribs are inclined to the radial direction, their radially inner ends can yield more easily in the radially outward direction. The radial stiffness can be adjusted through the degree of rib inclination. The ribs of the support structure and the bristles are preferably inclined in different directions with respect to the radial direction.
In another advantageous embodiment of the invention, at least one of the ribs is designed like a spring and/or at least one of the ribs runs in a straight line.
The spring-type design of the rib offers the possibility of the rib being elastically deformable in the radial direction. The ribs may be c-shaped or designed with a zigzag shape. A rib running in a straight line with an inclination to the radial direction also has a certain elasticity. The end positions of the ribs and/or the locations where the rib experiences a change in direction may act like solid-state joints which promote the spring property of the rib.
In another advantageous embodiment of the invention, an inner cover band is integrally molded on at least one rib directed radially inward. A plurality of ends of the corresponding ribs pointing radially inward may be integrally molded on an annular inner cover band.
As an alternative to this, each rib of the support structure may have its own inner cover band. Then the radial inner end of the rib may be arranged between the ends of the inner cover band arranged in the circumferential direction or the radial inner end of the rib is arranged on one end of the inner cover band arranged in the circumferential direction. For example, two, three or up to 40 ribs may also share an inner cover band, i.e., five radially inward directed ends of the corresponding five ribs may be integrally molded on a single inner cover band. All the inner cover bands are arranged one after the other in the circumferential direction and form a segmented ring. However, the inner cover bands may also form a closed inner ring.
In another advantageous embodiment of the invention, the support ring has an essentially annular mounting plate, which is arranged on the outside radially and on which the radial outer end of the support plate is arranged and/or on which the radial outer end of the support structure is arranged. The mounting plate may be segmented if needed. A brush seal can typically have an annular holding plate, which is arranged downstream from the bristles. Then the support ring and the holding plate clamp a c-shape wire ring with the bristles pointing radially inward.
In addition, preferred exemplary embodiments of the invention are described in greater detail on the basis of the schematic drawings.